/*
 * Copyright 2008 Sebastian Köhler
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 */
package net.dc.lib;

public class Base32 {
    private static final String base32Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";

    private static final int[] base32Lookup = { 0xFF, 0xFF, 0x1A, 0x1B, 0x1C,
	    0x1D, 0x1E, 0x1F,0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	    0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
	    0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
	    0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
	    0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
            0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
            0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
	    0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
	    0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
    };

    public static String encode(final byte[] bytes) {
	int i = 0, index = 0, digit = 0;
	int currByte, nextByte;
	StringBuffer base32 = new StringBuffer((bytes.length + 7) * 8 / 5);

	while (i < bytes.length) {
	    currByte = (bytes[i] >= 0) ? bytes[i] : (bytes[i] + 256); // unsign

	    /* Is the current digit going to span a byte boundary? */
	    if (index > 3) {
		if ((i + 1) < bytes.length)
		    nextByte = (bytes[i + 1] >= 0) ? bytes[i + 1]
			    : (bytes[i + 1] + 256);
		else
		    nextByte = 0;

		digit = currByte & (0xFF >> index);
		index = (index + 5) % 8;
		digit <<= index;
		digit |= nextByte >> (8 - index);
		i++;
	    } else {
		digit = (currByte >> (8 - (index + 5))) & 0x1F;
		index = (index + 5) % 8;
		if (index == 0)
		    i++;
	    }
	    base32.append(base32Chars.charAt(digit));
	}

	return base32.toString();
    }

    public static byte[] decode(final String base32) {
	int i, index, lookup, offset, digit;
	byte[] bytes = new byte[base32.length() * 5 / 8];

	for (i = 0, index = 0, offset = 0; i < base32.length(); i++) {
	    lookup = base32.charAt(i) - '0';

	    if (lookup < 0 || lookup >= base32Lookup.length)
		continue;

	    digit = base32Lookup[lookup];

	    if (digit == 0xFF)
		continue;

	    if (index <= 3) {
		index = (index + 5) % 8;
		if (index == 0) {
		    bytes[offset] |= digit;
		    offset++;
		    if (offset >= bytes.length)
			break;
		} else
		    bytes[offset] |= digit << (8 - index);
	    } else {
		index = (index + 5) % 8;
		bytes[offset] |= (digit >>> index);
		offset++;

		if (offset >= bytes.length)
		    break;
		bytes[offset] |= digit << (8 - index);
	    }
	}
	return bytes;
    }
}